Cardiovascular disease, including atherosclerosis, is a leading cause of death in the United States. In response thereto, the medical community has developed a number of methods for treating coronary heart disease, some of which are specifically designed to treat the complications resulting from atherosclerosis and other forms of coronary arterial narrowing.
The most significant and well-known development in treating atherosclerosis, as well as other forms of coronary narrowing, is percutaneous transluminal coronary angioplasty, more commonly known and hereinafter referred to simply as "angioplasty". The objective in angioplasty is to enlarge the lumen of the affected coronary artery by imparting a radially expansive force, typically accomplished by inflating a balloon, within the narrowed lumen of the coronary artery.
While the affected artery can be effectively enlarged via angioplasty, however, in some instances the vessel restenosis chronically, or closes down acutely, negating the positive effect of the angioplasty procedure. In such cases, such restenosis has frequently necessitated repeat angioplasty procedures or open heart surgery. While such restenosis does not occur in the majority of patients, it does occur with enough frequency that such complications comprise a significant percentage of the overall failures of the angioplasty procedure.
To lessen the risk of restenosis, various devices have been proposed for mechanically keeping the affected vessel open after completion of the angioplasty procedure. Such mechanical endoprosthetic devices, which are generally referred to as stents, are typically inserted into the vessel, positioned across the narrowed portion of the vessel, and then extended to keep the passageway clear. Effectively, the stent overcomes the natural tendency of the vessel walls of some patients to close back down, thereby maintaining a more normal flow of blood through that vessel than would otherwise be possible if the stent were not in place.
Various types of stents have been proposed and can typically be classed into one of two categories. In the first class, the stents comprise various tubular metallic cylinders expanded by balloon dilatation when positioned across the region or portion of vessel to be widened. In the second class, the stents are formed of a heat expandable material, such as nitinol or elgiloy, that are formed to assume a radially expanded state when deployed at the afflicted area within the lumen of the vessel. In this regard, such stents are typically delivered to the affected area on a catheter capable of receiving heated fluids, such as heated saline, such that once properly positioned, the heated fluid is passed through the catheter, thus causing the stent to expand.
Regardless of the class, significant difficulties have been encountered with all prior art stents. Each has had its percentage of thrombosis, restenosis and tissue in-growth, as well as varying degrees of difficulty in deployment. Another difficulty with at least some prior art stents is that they do not readily conform to the vessel shape and/or do not accommodate bifurcated blood flow caused by vessels having collateral vessels extending therefrom. Importantly, virtually all prior art stents suffer from the drawback of being structurally incompetent to withstand the stress and strain when the axially expansive, dilatory force is imparted thereto. This latter deficiency is especially problematic insofar as the incapability of such stents to withstand the stress of an axially expansive force may cause the stent to structurally deteriorate and axially constrict over time or, alternatively, migrate from the section of lumen where the stent was deployed.
As such, because of these and other complications, there has resulted a low level of acceptance of such stents within the medical community, and to date, such stents within the medical community have not been accepted as a practical method for treating chronic restenosis.
Thus, there has been a long felt need for a stent which is effective to maintain a vessel open, which may be easily delivered to the affected area, easily expanded to the desired size, easily conform to the afflicted vessel, capable of treating curved vessels with collateral vessels extending therefrom, as well as withstand the stress and strain when an axially expansive force is imparted thereto.